Hybrid electric vehicles (HEVs) include an internal combustion engine, one or more electric machines, and a traction battery that at least partially powers the electric machine. Plug-in hybrid electric vehicles (PHEVs) are similar to HEVs, but the traction battery in a PHEV is capable of recharging from an external electric power source. Generally speaking, both HEVs and PHEVs are capable of operating in an electric-only mode with the engine off. Thus, the engine may stop and start in response to various operating conditions during a drive cycle, including battery state of charge, climate control requirements, and electric accessory draw.